This invention relates to integrated circuits, and more particularly, to fuse programming and sensing circuitry on integrated circuits.
It is often desirable to be able to make adjustments to the circuitry in integrated circuits. For example, programmable integrated circuits contain programmable logic that is configured by loading the circuits with configuration data. This allows circuit designers to implement custom circuit designs in the programmable integrated circuits.
Some adjustments can be made using nonvolatile memory elements. For example, an integrated circuit may contain nonvolatile memory elements based on polysilicon fuses. The fuses may be programmed using current pulses. Sensing circuitry may be used to sense the programming state of the fuses. Output from the sensing circuitry may be used to control circuitry on an integrated circuit.
Fuses and other nonvolatile memory elements may be used to store permanent configuration settings. For example, following testing of an integrated circuit, it may be desired to permanently switch redundant circuitry into place to repair defective circuitry. In this type of situation, fuses may be programmed to configure switching circuitry on a device. Because the fuses are nonvolatile, a repaired integrated circuit can be shipped to an end user in an unpowered state. When the integrated circuit is incorporated into a system and powered for normal operation, the repair configuration data that is stored in the fuses will configure switching circuitry on the integrated circuit so that appropriate redundant circuitry is switched into place to repair the defective circuitry.
Fuses may also be used to store other data on an integrated circuit. This data may include, for example, manufacturing data such as a serial number or other identifier and security data such as a secret code.
It may be desired to limit access to fuse-based control circuitry and circuitry that is involved in other integrated circuit control operations. For example, it may be desirable to limit access to fuse settings, because fuses may contain sensitive data. It may also be desirable to limit access to control circuitry on an integrated circuit that has the potential for being misused.
To prevent unauthorized access to sensitive circuit functions and fuse settings, it would be desirable to be able to provide fused-based circuitry with enhanced security features.